#include<stdio.h>
#include<math.h>

#define HELEN(a, b, c) sqrt((a+b+c)/2*((a+b+c)/2-b)*((a+b+c)/2-c)*((a+b+c)/2-a))
int main()
{
  int a, b, c;
  scanf("%d%d%d", &a, &b, &c);
  printf("%f\n", HELEN(a, b, c));
  return 0;
}

//#define max(a, b, c) (a > b) ? ((a > c) ? a : c) : ((b > c) ? b : c)
//#define sum(x, y) (x + y)
//
//int main()
//{
//  int a, b, c;
//  float d, e;
//  printf("Enter three int:");
//  scanf("%d%d%d", &a, &b, &c);
//  printf("\nthe max of the is %d\n", max(a, b, c));
//  printf("Enter two float:");
//  scanf("%f%f", &d, &e);
//  printf("\nthe sum of them is %f\n", sum(d, e));
//}
